Remove old context.
Remove two contributors that have unknown controbutions.

http://root.cern.ch/viewvc?view=rev&revision=47341 does not motivate it;
they do not show up in CREDITS.
Do not force the load for updating existing TClasses.
Merge Ctors from nested transactions.

We cannot run nested transactions' initializations until the parent is done.
But the parent transaction must not replace the nested transactions' static initialization either.
The only way out is to collapse all transactions' static initializers until they are run.
This fixes
root [0] TTree *chain = new TTree("abc","title")
which left chain == 0 before.